1. Field of the Invention
This invention relates to an underwater housing, and more particularly to an underwater housing for containing a monitoring device, such as a photographic camera, that provides monitoring for long periods of time.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional underwater housing 1 for containing a photographic camera (not shown) includes a tubular housing body 11, a seal cap 12 connected fixedly to a rear end of the housing body 11 so as to define an accommodating space 10 for receiving the photographic camera, a transparent plate 13, a positioning member 14, and a water seal 15. The photographic camera can be used to monitor living creatures (e.g., fish) via the transparent plate 13.
The housing body 11 has a surrounding wall 16 and an annular front end wall 17 formed with an internally threaded portion 171 and a central opening 172. The photographic camera is disposed within the surrounding wall 16. An inward flange 170 extends radially and inwardly from a front end of the front end wall 17, and has a rear side surface formed with an annular groove 173 for receiving the water seal 15. The positioning member 14 has an externally threaded outer periphery engaging the internally threaded portion 171 of the housing body 11. The transparent plate 13 is clamped between the positioning member 14 and the water seal 15. The water seal 15 is in contact with the transparent plate 13 and the inward flange 170 so as to establish a watertight seal between the transparent plate 13 and the housing body 11. An electrical cable 18 extends sealingly through the seal cap 12, and is coupled electrically to the photographic camera.
Typically, the underwater housing 1 is placed at a specific location underwater for more than six months. Since an annular gap is formed between the transparent plate 13 and the inward flange 170, algae easily grow on a front side surface of the transparent plate 13, as shown in FIG. 2. This adversely affects the quality of the images obtained by the photographic camera.
To remove the algae on the transparent plate 13, it is necessary to first take the housing 1 out of water to gain access to the transparent plate 13. Alternatively, a diver or snorkeler may swing underwater to the housing 1 to shave off the algae and scrub the front side surface of the transparent plate 13 using tools. However, in either case, since algae multiply at an extremely fast pace, the labor costs involved in ensuring that the transparent plate 13 remains algae-free are high.